Electric furnace



`lune l2, 1928. 1,673,543

E. wlRZ ELECTRIC FURNACE June 12, 1928.

E. wlRz Filed May 14, 1927 SSheets-Sheet 2 u June 12, 192s. 1,673,543

E. WlRZ ELECTRIC FURNAGE Filed May 14, 1927 3 Sheets-Sheet 3 Patented June 12, 1928.

UNITED STATES ERNST WIRZ, OF BADEN, SWITZERLAND,

' PATENT OFFICE.

ASSIGNOR TO AKTIENGESELLSCHAFT A. G.

BROWN BOVERI & CIE., OF BADEN, SWITZERLAN1),A JOINT-STOCK COMPANY 0F SWITZERLAND.

ELECTRI- FUBNAGE.

Application led May 14, 1927, vSerial No. 191,434, and in Germany May 19, 1926'.

This invention relates to electric resistor furnaces and it has among its objectsthe provision of a furnace ofthe foregoing type having improved resistor heating units adapted to be individually removed from the furnace without serious interference with the operation of the furnace.

In resistor-type furnaces that are operated Y on relatively low voltages, Y

resistor elements are used. Accordingly, the individual resistor elements do not require complicated supporting arrangements within the furnace in order to take up the variations of the length of the elements' caused by expansion or contraction under temperature changes.

It is otherwise, however, in furnaces in which the individual resistor elements are supplied from la relatively high voltage 20. source. In such cases, the resistor elements M are formed of relatively thin, flexible wire yor ribbon, which does not have any inherent stiffness that would prevent it fromestab-- lishing contact with the adjacent resistor elements when expanding under high temperature conditions.

According to vthe invention, the diiiiculties in providing heating units for high voltage service of the foregoing type are avoided by having the convolutions or loops 'forming the resistor element" suspended in the fur- 'nace chamber, with na spacing member for insulatingly separating the lower ends of said loops or convolutions so arranged that such spacing member weighs upon said loops and holds the same taut. Such construction permits free expansion or shrinkage lof the resistor loops, and, at the same time, eectively prevents contact between adjacent elements of said loops.

The foregoing and other features of the invention will be best understood from the following descriptions of exemplifications thereof, reference being had to the accompanying drawings wherein i Fig. 1 is a vertical sectional view through a furnace embodyingone form of the invention;

relatively rigid` is anf elevational vview of the re-v movable side Fig. 1;

Fig. 3 is va view similar to Fig. 2 of a heater unit embodying another form of the invention;

Fig. et is a sidefelevational view of the heater unit inFig. 3; Fig. v5 is a view similar to Fig. 2 illustrating a heater unit embodying a still further modification of the invention;

Figs. 6 to 8 are fragmentary horizontal sectional views illustrating different forms of the lateral guide support of a heater unit such as shown in Fig. 5;

F ig.l 9 is a view similar to Fig. 2 of still another form of the invention;

Fig. 10 is a side view of theheater unit in Fig. 9;

Fig. 11 is a top view of the floor heater unit of the furnace in Fig. 1; I Fig. 12 is a front elevational view of a laterally removable heater element of the rear wall of the furnace in Fig. 1;

Fig. 13 is a vertical sectional view through the heater unit in Fig. 12 along the line 13-13; and l Figfll is a view' similar to Fig. 12 illus-V trating a modication of the invention. Referring to the drawings, a furnace exemplifying the invention comprises a furnace chamber 1 formed of refractory side walls 2, a floor or bottom wall 3, a roof or cover' wall 4 and rear and front walls 5. The walls are formed of a suitable heat resistant material that is both'v an elect-ric and heat insulator as is known in the art. In theusual constructions, the walls are vmade of bricks, the inner .part of the walls facing the chamber being of a highly refractory re brick or similar material.

The furnace is arranged to be heated by a Vpluralit of: heater units which are so mounte as topermit ready removal of the individual units without materially interfering with the operation of the other units or the furnace. This may be best effected by constructing the individual heater units so Vas to be suitable for direct parallel connectionl'to the relatively high-voltage supply heater unit of the furnace in .source which is usually available without experienced in manufacturing such heater units suitable for high voltage operation on account of lack of stiffness of the relatively thin resistor ribbon whichv must be used in constructing the unit. These ditliculties are avoided by making the heater units according to the invention as described hereinafter.

The'heater units used the furnace of Fig.. 1 are. of three different types-the side heater units 6 adapted to be placed along the side walls 2 in the` interior of the chamber;

the floor heater units 7 adapted to be placed at intervals along the floor walls 3 of the furnace chamber; and rear or front wall heater units adapted to be placed' beside the rear or front walls of the chamber. These different heater units and their mounting in the furnace will now be discussed.' f

The side heater units 6 are each formed of a refractory supporting member 11 in the form of an elongated bar or brick of refractory material. The bar 11 fits into a suitable slot in the top wall of the furnace chamber and constitutes a part of the furnace walls. In the construction shown in the drawing, the bar 11 rests on ledges 13 of the side wall and roof, respectively, of the furnace chamber, said ledges preventing the bar from dropping down. Verticallyextending through the bar ll are two-metallic supporting rods 15, said rods beingsuitably molded in or otherwise secured and held in tixed position in said bar. On thetdownwardly extending portions of the rods" 15 there are mounted two transverse refractory resistor supporting plates 16 and 17, said plates having vertical perforations-18 adapted to slide over the two rods 15. The plates are provided with projections or studs 19- over` which are' wound a plurality of the heater loops 20 of a resistor wire or ribbon, the two ends of the ribbon'being attached to the two supporting rods 15 at 21, thereby establishing a connection to the exterior of the fura nace. By connecting the outer ends of the two rods 15 to. the source of supply, as by means of terminal nuts 22, an electric current may be-conveniently supplied to said resistor loops 20 for heating the same.

The upper supporting plate 16 is held at a fixed height within the chamber and prevented from sliding down on the supporting rods 15 by means of discs 23 welded or otherw1se secured to said rods under the lower heater unit may be readily removed and reer resistor plate will, by its own weight, hold It-he individual loops in taut condition. Since the individual loops are joined together and constitute a single continuous strip freely .'der the weight of the lower supporting plate 17l so as to maintain all the elements of the loop under substantially thesame tension.

As a result, the difficulties encountered in prior art constructions on account of the changes in the length of the resistor elements with the variations of the temperature are completely eliminated. Under no conditions will adjacent loop elements come into contact with each other, 'or 'excessive tension'beintroduced into the structure.

In the form of invention shown inT Figs. l

1 and 2, the plates are provided with -substantially verticalwebs or ribs. 27 extendinginto the space between the loops so as to pre' vent accidental contact-between adjacent loop portions in case the latter should, for some unforeseenzrcason, become too slack and not supporting plates. A

In the modification of the invention shown follow the'tensioning vaction of the lower f in Figs. 3 and 4, theheater unit-comprises a block 31 extending` and 'supported within a narrow slot at the top wall of the furnace chamber as in the construction of Figs. 1

Iand 2. AA pair of strips 32 of a suitable-refracftory alloy metal have their upper ends embedded in the block 31 and serve to carry two supporting traverses 33 similar to the.

plate 16 in Figs. 1 and 2. The traverses 33 are. each formed of-a strip -of refractory metal bent to form an` elongated rectangular frame lhaving its two narrow sides titting the two downwardly extending supporting strips 32. The upper traverse 33 is suitably secured, as by welding, to the supporting strips 32 and carries a plurality of rollers 35 of insulating material over which the heater ribbon may be wound. The lower traverse 33 is freely slidable on the supporting strips 32 and Valso carries a plurality of rollers 35. A resistor lribbon 36 is wound on said rollers to form ra plurality of heater loops, the two ends of the ribbon being connected to lead-instuds 37 extending through the bar 31. for making electrical'connections to said heater ribbons 36 from outside* of the furnace. As in the. case of the construction in Figs. 1 and v2, 'the weightA of the lower traverse 33 will cause .self alignment of thel individual resistor loops'andfhold said loops :in taut condition. In the foregoing constructions, a damaged placed by simply lifting the block- 11 or 31 with thevheater element held on the frame supported from said block, and replacing `it by another similar heater unit, without interfering with the'operation of the furnace.

-In Figs. 5 and 6 is shown a form of the izo invention wherein the removable heater unit does not constitute a relatively rigid frame as in the forms of the invention described hereinabove, but constitutes a set of loops freely suspended from the removable block on the top of the furnace chamber, said loops being held in spaced relationship by a guide member or plate which is suitably supported within the furnace chamber inde- Y assembled. A plurality of such blocks 52 pendently of the supporting members of the loop. `As shown in the drawings, the removable block 31 held in the slot on the top wall of the furnace chamber, carries at its inner side a loop supporting member 41 having a plurality of projectionse42 over which the resistor loops 43 may vbe wound. Into the lower bights of the loopsextend a plurality of projections 44'of a Guide plate 45 similar to the lower plate ofF ig. 2, said guide plate having at its two ,side ends engagement with suitable cooperating guiding grooves 46 on the side walls of the furnace chamber. Said side grooves may be of various shape, as shown in Figs. 7 and 8 for instance.

In Figs.` 9 and 10, is shown another form of a side wall heating element. In this construction the refractory block 11 carries a pair of support-ing rods 51 of refractory ma` terial. On said supporting rods are threaded a lplurality of insulating blocks 52, said blocks having a central vertical perforation 53 fitting over the rod.' Each block is provided with a plurality of horizontal perforations 54, extending on both sides of the vertical perforations. Within corresponding horizontal perforations of opposite blocks held on the two supporting rods 51 areV mounted transversely disposed refractory tubes 55 over which a resistor wire 56 is wound in the form of a helix. A relatively.

large amount of resistor material may thus 'be accommodated wit-hin a relatively small space and by reason of the simple construction of the elements of whichI the heating unit is built up, heater units of different capacities may readily be manufactured and are assembled, one ontop of the other, on

,each of the supporting rods 51, land are locked or supported in place by means of a suitable clip 56, clamped on the lower end of the supporting rods. The horizontal perforations for mounting the transverse r'- fractory resistor elements are preferably staggered to provide favorable heat radiating conditions within the furnace chamber.

The floor heater element 7 of Fig. 1, referredto, a .plan view of which is shown in Fig. 11, is also ofthe removable unit type.

' It comprises a block 61 of refractory mate- -rial fitting vinto ay suitable slot in the side yWall of the furnace chamber and thus constituting in itself a. portion ofsaid side wall. Within the side block are embedded a pair transverse plates having perforations for4 receiving a series of refractory insulating tubes 66 over which a resistor wire is Wound in the form of a helix. The individualv resistor units 66 are suitably interconnected to two terminal studs' 67 Vextending' through the side block for making external connections to said resistor elements. The entire heating unit may be readily withdrawn for-rcplacement or repair Without interfering with other elements of the furnace. A similar construction may also be used as a heater Enit on the roof wall of the furnace cham- A construction ,of the type utilized in the floor heater element of Figs. 1 and 11 may also be utilized for .heater units that are to extend vertically inside vthe chamber, but which are not to be suspended from the roof wall thereof. A construction of suoli character is shown in Figs. 12 and 13, as applied Vsaid block by means of bolts 74 which also serve as external connections to the resistor elements. The opposite Walls of the bars are provided with perforations 75 for receiving refractory tubes 76 over which is wound a helical resistor wire 77 for heating the furnace. With such construction a portion of the side Wall of the furnace corresponding to the width of the heater unit, must be made removable as shown'at 78, in orderv to permit the passage of 'the frame carrying the resistor elements. A suitable duct 79 underneath the supporting block 71 is p-rovided for the electrical connections to the resistor elements.

In the form of the invention shown in Fig. 14, a resistor structure of the type shown in Figs. 3 and y4 is supported ona frame unit vof the type utilized in the floor heating unit IUU frame. Between opposite sides of the bars 83 are mounted traverses 85 for supporting a plurality of resistor loops as described above.-

The foregoing constructions permit the removal of the heating units eitherfrom the top or fromv the sides or from the bottom of t-he furnace chamber. The choice of particular construction of the heating units Will depend ou the particular conditions for which the furnace is built. Fr example, when a number of furnaces are to be arranged side by side, heater units that are to -claims be given a broad construction.

I claim:

1. An electric resistor heater comprising a continuous resistor heating element wound :into a plurality of loops, a pair of spaced supporting members engaging the opposite bights of said loops, said loops being loosely mounted on said members and held stretched thereby, and guide rods engaging said members to permit sliding movement of one of said members with respect to the other.

2'. In an electric resistor furnace having a plurality of refractory walls enclosing a furnace chamber, a heater comprising a refractory block removably mounted in a slot on the wall of said chamber, a pair of supporting rods secured to said block and extending into said chamber, a pair of transl verse members mounted on said rods, one of said members being slidable thereon,l a resistor wire Wound between said transverse members to forma plurality of loops having their bights supported by said members, said heater being so mounted within said chamber that the slidable loop-supportingk member Weighs on said loops and holds the same 1n stretched condition.

3. An electric resistor furnace having a plurality of refractory walls enclosing a furnace chamber, a heater unit comprising a refractory block mounted in a slot on the'top wall of said chamber and constituting a por` tion of said wall directly communicating with the interior of the chamber, a heater wire wound into a plurality of loops suspended from said block into the interior of said chamber, a refractory insulating member spacing the lower bights of said loops and weighing thereon to hold said loops in taut condition.

4. An electric resistor furnace having a plurality of refractory walls enclosing a furnace chamber, a heater unit comprising a refractory block mounted in a slot on the top wall of said chamber and constitutinga por tion of .said wall directly communicating with the interior of the chamber, a heater wire wound into a plurality ofloops sus-l pended from said block into the interior of said chamber, a refractory insulating mern- Y ber spacing the lower bights of said loops and -weight-ing thereon to hold said loops in taut condition, and means for guiding said member in definite relationship to said block.

5. An electric resistor furnace having a. plurality of refractory walls enclosing a furnace chamber, a heater unit comprising a refractory block mounted in a slot on the top wall of said chamber and constituting a portion of said wally directly communicating with the interior of .the chamber, a heater wire wound into a plurality of loops suspended from said block into the interior of said chamber, a refractory` insulating member spacing the lower bights of said loops kand weighting thereon to hold said loops in taut condition, and guide rods 'extending from said block for guiding. said tensioning member relatively thereto.

4 6. In an electric resistor furnace having a plurality of refractory walls enclosing a furnace chamber, a heater unit comprisingva relatively narrow block of refractory 'insulating material removably mounted in a slot of said wall and constituting a part of the enclosure of said chamber, a pair of refractory metallic supporting rods mounted on said block and extending into said chamber from the exterior of the'furnace, a transverse supporting member extending between said supporting rods and constituting in conl junction therewith and with said block a unitary frame removable from said furnace through said slot, and a resistor wire mounted on said frame, said resistor wire having its ends connected to said rods for receiving current from the exterior of said furnace.

7. In an electric furnace, a heating unit extending into and removably associated with the same; said unit including a blocli formi part of and having a free itwvith respect o a wall of said furnace for movement outwardly'away from said wall, a plurality of elements supported within said furna( a and associated with said block for such.

movement therewith and spaced and arranged to form a row, a plurality of ele-r ments disposed within said furnace below said first-named elements and spaced and arranged to form a lower row complementary to the upperv row, and a resistor member extending from one end to the other of said rows and alternately around the op-A positely-disposed and respective elements of to expanding and contracting action of said the upper and lower rows to form verticelly-v resistor member. v

disposed loops providing a suspending sup- In testimony whereof I 4have hereunto 10 port for the lower elements from the upper subscribed my name at Zurich, Switzerland, 5 elements such as to Apermit of relative vertithis 2nd day of May, A. D. 1927.

cal movement of the upper and lower elements with respect -to` each other consequent f ERNST WIRZ. 

